Process and device for cleaning the waste air of systems for the solidification of melts

ABSTRACT

A melt is converted into pieces by being converted to individual quantities that are dropped onto a cooling surface. Disposed above the cooling surface is a hood having a suction outlet for conducting waste air to a cleaner. Disposed in the hood upstream of the suction outlet is an arrangement of surfaces defining a serpentine flow path for the waste air so that a vaporous component of the waste air crystallizes on the surfaces. The surfaces are formed by plates mounted on a common transport carrier which periodically moves the plates against a scraper for scraping off the crystallized material. Alternately, the surfaces can be defined by endless belts which move against scrapers.

BACKGROUND OF THE INVENTION

The invention relates to a process and a device that accommodatecleaning the waste air of systems that accommodate the solidification ofmelts, which melts are deposited on cooling surfaces, in particular acooling conveyor and harden there, especially systems for solidifyingsulfur.

It is well-known that a series of products, such as resins, adhesives,or the like, but also sulfur can be made transportable and handlable bymelting them and depositing them either in strips or in the form ofdrops on a moved cooling belt, where the melt hardens. If said melt isdeposited as drops, the result at the end of the cooling belt is agranulate that can be packaged. If deposited as strips, said stripsbreak into pieces and can also be packaged.

Since vapors, which can be environmentally endangering, are producedwhen the melt is deposited, in particular in the case of sulfur, it iscustomary to use suction devices which ensure that the resulting wasteair is removed and cleaned in a defined manner. The cleaning is donewith the aid of filters, which are relatively expensive. There is alsothe specific drawback with the known cleaning process that the amount ofdust that is removed with the waste air is lost to the production of theproduct.

SUMMARY OF THE INVENTION

The invention is based on the problem of designing a process and adevice of the aforementioned kind in such a manner that a smaller amountof the product gets into the waste air so that the burden is taken offof the cleaning process that takes place there.

To solve this problem, the process of the invention proposes that aportion of the product produced as vapor behind the feed point of themelt is removed by crystallization prior to the removal of the waste airand is removed as a solid component. With this measure it is possible toavoid a large portion of the by-product that is produced otherwise asdust and under some circumstances to use the crystallized output againfor processing the melt. In so doing, in an improvement of the inventiveidea the size of the crystallization surfaces provided for thecrystallization process are adapted to the vapor pressure profile overthe product, so that where higher vapor pressure prevails, there is alsothe possibility of depositing larger quantities of the product in theform of crystals on the surfaces.

To implement the new process, a device with a suction hood, which isarranged over a cooling belt and which covers a feeder for the melt andexhibits a suction fitting, can be provided. In the region between thefeeder and the suction fitting the hood is provided with installations,which project into the waste air flow and are intended for thecrystallation of the product and in the region of the installations saidhood is provided with regulatable openings for producing a specific airflow. This design allows the flow rate of the waste air in the region ofthe installations to be chosen in such a manner that there is adequatetime for the crystallization at the installations. At the same time theinstallations can be designed in an especially simple manner as wallsthat are arranged in the manner of a labyrinth at right angles to thewaste air flow. Therefore, the waste air flow is forced to flow alongthe walls and in particular at a defined velocity, so that the desiredcrystallation occurs. To promote the crystallization process, the wallscan also be made of heat conductive material and provided with channelsfor the passage of a thermostatable heat exchange medium or, whosetemperature can be stabilized in some other manner. In this manner it ispossible to design the temperature of the crystallization surfaces insuch a manner that the conditions are optimal for crystallization.

To achieve an adaptation to the vapor pressure profile over the product,the walls can be parallel and at different intervals in the direction offlow; said intervals being adapted to the vapor pressure profile overthe product. The walls can project vertically beyond the hood cover intothe flow. They can also project horizontally from the opposite sidewalls of the hood into the flow and in particular in such a manner thatopposing flow gaps, which result in flow circumventing the walls servingas the crystallization surfaces, are designed along the line of alabyrinth.

To remove at specific intervals the product that has crystallized on thewalls, it is advantageous to attach the walls rigidly to transportelements, which enable the walls to be moved sideways out of the hood,whereby the walls exhibit adapted stripping openings in the region ofthe side walls of the hood, from which the crystallisate can be scraped.The walls can be pulled out by hand or also automatically at specifictime intervals, e.g. by means of pneumatic or hydraulic cylinders oralso by means of drive motors for the purpose of cleaning. In any casethe construction is designed in such a manner that the crystallizationsurfaces of the walls are not thoroughly cleaned, in order to leavecrystal nuclei, which promote the crystallization at the renewedstartup. An especially simple possibility of the configuration of thewalls results when the walls themselves form transport elements and aredesigned as one belt or several infinite belts, which traverse the hoodat right angles to the direction of flow and traverse at the side wallsof the hood the stripping slots and the slots between the temperingplates, which in turn provide for a tempering of the continuous belts,which form the crystallization surfaces. The circumferential speed canbe chosen to match, so that a continuous cycling is possible. Naturallyit would also be possible to move the belts discontinuously. In any casethere is the possibility of collecting and removing the crystallizatethat is scraped off. For example, it can be fed again to the processingof the melt for product manufacturing. With this design it is possibleto avoid from the start a significant amount of dust content in thewaste air. Thus, the cleaning systems for the waste air can beunburdened.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is depicted in the drawing and is explained in thefollowing with reference to embodiments.

FIG. 1 is a schematic drawing of an apparatus for the production ofgranulated material from a melt, including a waste air suction device.

FIG. 2 depicts a section of the device of FIG. 1 with a revolvingcooling belt, a feeder for the melt and the crystallization surfacesaccording to the invention.

FIG. 3 is an enlarged detail of a first embodiment of thecrystallization walls of the device of FIG. 2.

FIG. 4 is a perspective drawing of a modification of the crystallizationwalls of FIG. 3.

FIG. 5 is a top view of a section of the hood of the device of FIG. 2and the respective crystallization walls.

FIG. 6 is a drawing similar to FIG. 5 of an embodiment havingcrystallization walls which can be moved sideways out of the hood.

FIG. 7 depicts an embodiment of a device wherein the crystallizationwalls are designed directly as belts traversing the hood.

FIG. 8 is a drawing similar to FIG. 3, but with crystallization walls,which project sideways beyond the walls of the hood and are offset inthe interior of said hood; and

FIG. 9 is a top view similar to FIG. 5 of the embodiment of FIG. 8.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 depicts, first of all, quite generally a system, in which a melt,for example molten sulfur, can be processed into pellets. For thispurpose the system according to FIG. 1 has a cooling belt (1). Coolantis fed through a line (2) into a chamber (3), below a carrying run orflight of the cooling belt (1) and is sprayed, for example, usingspraying nozzles, against the side of the cooling belt (1) which isdesigned as a steel strip. The coolant is recycled by means of a drainline (2a).

The cooling belt (1) is guided around two deflecting rollers (4) andruns clockwise in the embodiment. Above the carrying run of the beltthere is a suction hood (5), which exhibits a suction fitting (6)attached, as shown only schematically, via a suction line (7) to asuction fan (8), to which a cleaning filter (9) or the like is alsoconnected in series in the embodiment.

Molten sulfur is fed through the feed line (10) to a well-known rotorformer (11), which comprises in essence two telescoped pipes, of whichthe inner pipe, which is tempered and filled with melt exhibits adownwardly oriented slot, and the outer pipe is provided with openingsover its entire circumference. In the embodiment the outer pipe rotatescounterclockwise around the inner pipe; and thus the sulfur melt isdeposited in the shape of drops on the upper side of the cooling belt(1), so that the drops can harden there into solid pellets. At the endof the cooling belt (1) these pellets are conveyed over a slide (12)onto a belt (13), which is shown only schematically. By means of thebelt (13) the pellets move into a collecting tank (14) and can be putthere into commercial packagings. This process has the basic advantagethat the sulfur already exists as pellets and does not have to be brokenout first from a thoroughly hardened layer into a pourable product, asis also well-known. In such a process the breaking of the sulfur cakesgenerates a significant amount of dust, which is to be avoided from anenvironmental point of view.

As the molten sulfur is deposited by means of the rotor former (11) onthe cooling belt (1), however, a vaporous sulfur, which appears assulfur dust in the region below the hood (5) due to the subsequentcooling, is also produced. The essence of the invention is to avoid thecreation of this sulfur dust, which is extracted through the fitting (6)and has to be removed from the waste air in the filter (9).

According to the invention, the hood (5)--which will be explained indetail with reference to FIGS. 2 and the following Figures--is providedin the region between the rotor former (11) and the fitting (6) withinstallations (15), which are disposed within the flow generated by thesuction fan, above the cooling belt (1). Each installation (15)comprises labyrinthine baffle plates 17 for conducting the flow; saidbaffle plates force the flow to flow in a serpentine path to the fitting(6). In addition, the hood (5) is provided, on the other side of thefitting (6), with openings (16), whose cross section can be regulated.The openings (16) serve to divide the amount of waste air, which isconveyed from the fan (8) through the fitting (6), in a specific andcontrolled manner into an amount coming from the right and left sides ofthe hood (5) and into an amount coming from that section of the hood (5)that lies to the right of the fitting (6). Thus, with this measure it ispossible to control the flow rate of the waste air in the section lyingbetween fitting (6) and rotor former (11). This means, that the flowrate of the waste air in the region of the installations (15) can beadjusted by suitably regulating the size of openings (16).

FIGS. 3 to 5 depict a first example of the installations, which are usedin the hood (5) to enable one portion of the product, which is producedas vapor behind the feed point (rotor former (11)) of the melt, tocrystallize out while allowing the removal of the waste air. FIGS. 3 and4 show that in a first embodiment for this purpose the hood (5) hasinstallations in the form of parallel, flat walls (17), whose mutualspacings a-d in the travelling direction of the cooling belt (1) becomesincreasingly larger. Between the first two walls (17), which are formedas plates, there is the distance (a); between the next two walls thedistance (b), then the distance (c) and finally the distance (d). Thesecontinuously increasing distances are adapted to the vapor pressureprofile over the product, which is located on the cooling belt (1).Thus, the goal is reached that the surfaces of the walls (17) in theregion of the high vapor pressure have a larger total cross-sectionalarea than in the region of the lower vapor pressure. If at this stagecare is taken that the flow rate of the waste air is chosen to match, asaforementioned, then the sulfur will crystallize on the surfaces of theplates (17). For this purpose, as shown in FIG. 4, the plates (17) canalso be provided with channels (18), to which a coolant is fedexternally through the line (19) and drained again through the line(20). If the plates (17) are made of heat conductive material, thentheir surface can be tempered. Naturally it is also possible to temperthe plates (17) in a different manner, e.g. externally by means of heatconduction. The temperature can be chosen in such a manner that thecrystallization process can take place as optimally as possible.Therefore, the invention provides the possibility of letting the bulk ofthe sulfur, produced as vapor behind the rotor former through thedelivery of melt, crystallize out on the surfaces of the plates (17), sothat this vaporous sulfur does not become dust due to subsequent coolingand, therefore, does not get into the filter (9). Rather it remainsfirst in the crystallized state on the surfaces of the plates (17) andhas to be removed from there from time to time.

For this purpose a first embodiment according to FIG. 5 (and 3 and 4)provides that the plates (17) are attached all together to a carrierplate (21), which can be slid at right angles to the travellingdirection of the cooling belt (1) in the hood on corresponding guides(5a), which are integrated (in a manner that is not illustrated indetail) into the cover of the hood (5), into the end position (21'),shown in FIG. 5). The device is designed in such a manner that astripping wall (22) with slots (23) is attached to the hood (5) at theside of the cooling belt (1). The size and mutual distance of saidstripping wall is adapted to the condition and to the dimensions of theplates (17). In front of the stripping plate (22) there is a chamber(24), which can also be designed as a separate suction chamber. If,therefore, the plate (21) is pulled (e.g., manually) with the plates(17) attached thereto into its position (21') outside the hood (5), thenthe cystalline sulfur, adhering to the surface of the plates (17) isscraped from the slots (23) and falls into the chamber (24). From thereit can be removed and conveyed, for example, to the processing devicefor the sulfur melt. The slots (23) serve to strip and scrap off thecrystalline sulfur. However, they clean the surfaces of the plates (17)in such manner that the crystal nuclei still remain on the surfaces.When the plates (21) are pushed back again and when the plates (17) arereconfigured in the flow path, said crystal nuclei ensure that thesulfur vapor will continue to crystallize out.

FIG. 6 shows a variation of the embodiment of FIGS. 3 to 5, insofar ashere the plates (170), which can be arranged, moreover, in the samemanner as the plates (17) of the embodiment of FIGS. 3 to 5, areattached to a common plate (210), which is significantly wider than thehood, whose side boundaries terminate in the side edges of the coolingbelt (1). In this embodiment the plates (170) are guided in slots (230)in two side plates (220), which are arranged parallel to both the outeredges of the cooling belt (1) and the side walls of the hood. In thiscase, too, there are collecting chambers (240) within the guide plates(220), which can serve to hold the sulfur scraped off the slots (230).

The plates (170), guided in the slots (230) on both sides in thisembodiment, are attached to a common plate (210); and this plate (210)can be slid back and forth in the direction of the arrows (26) by meansof pneumatic cylinders (25), which are mounted on both sides, in such amanner that said plate protrudes to one side around the dashed region(210'). In this position a section of the surfaces of the plates (170),located in the waste air stream within the hood (5), can be scraped offand cleaned, as described in connection with FIGS. 3 to 5. The movementin the direction of the arrows (26) can take place intermittentlyautomatically at specific intervals. A continuous back and forthmovement, which would have to occur at corresponding rates, would alsobe possible.

FIG. 7 shows another embodiment. Here, instead of the plates beingattached rigidly to a carrier, three revolving endless belts (27) areprovided as the crystallization surfaces. Said belts are guided onrespective reflecting rollers (28) at right angles to the travellingdirection of the cooling belt (1). Furthermore, the belts (27) have totravel within the chamber in the suction hood (5) (not illustrated) and,therefore, must be designed in such a manner that the course of thebelt, shown in FIG. 3, is also labyrinthine between the individualbelts, said course forcing the waste air flow to flow from the bottom tothe top and again from the top to the bottom through the baffles, formedthen by the belts (27). The belts (27) leave the hood through plates(29) on the one side and plates (30) on the other side, to whichcollecting chambers (31) are assigned on the side facing the coolingbelt (1). These plates (29 and 30) contain the scrap-off slots, whichexert the same function as the slots (23 or 230) of the designsdescribed above. In addition, the revolving belts (27) also have coolingplates (32) upstream of the entry into the interior of the suction hood.Said plates are designed in such a manner that the belts are guided inslotted openings and, in so doing, make thermal contact with the coolingplates (32). In this manner, too, it is possible to temper in such amanner the continuously revolving belts, which can be, for example,metal belts that the desired crystallization process is optimal.

Finally FIGS. 8 and 9 show a variation of the plates (35), projectinginto the waste air flow, insofar as here the plates (35) are alsoattached to a common plate (34), which can be removed from the hood (5)in the direction of the arrow (36), but in such a manner that thelabyrinthine gaps for the flow are not formed at the top and the bottomof the plate, but rather on offset sides of the plates (35). It isapparent that the waste air flow is forced here to escape to the side inthe direction of the arrows (37), and then flows parallel to the plates(35) to reach the next side in order to eventually leave the labyrinththrough the suction fitting. Of course, such an arrangement can also beused in an advantageous manner for crystallizing sulfur vapor. In thiscase the flow paths of the waste gas between the plates (35) areelongated, so that the sulfur vapor has adequate time to crystallize.The mutual distance between the plates matches that of FIG. 3. Moreover,a stripping plate (22) is also provided here, as in the embodiment ofFIG. 5; and the plates (35) can be stripped of the crystalline sulfur,adhering to their surfaces, when their transport plate (34) is pulled inthe direction of the arrow (36). Said sulfur then falls into thecollecting chamber (24).

We claim:
 1. A process for cleaning waste air generated during thesolidification of a molten material comprising the steps of:A)converting the molten material into individual quantities which arepositioned on a cooling surface for solidification; B) collecting, in aspace formed above the cooling surface, waste air which contains avaporous component emanating from the material; C) conducting thecollected waste air from the space to a cleaner; and D) causing at leastsome of the vaporous component to crystallize on surfaces located withinthe space prior to step C.
 2. The process according to claim 1, whereinstep D comprises passing the waste air across the surfaces of plateswithin the space.
 3. The process according to claim 2, wherein step Dcomprises conducting the waste air in a serpentine travel path definedby said plates.
 4. The process according to claim 2 further includingthe step of periodically scraping crystallized material from saidplates.
 5. The process according to claim 2, wherein step D comprisesproviding a greater concentration of said plates in a region of thespace where the pressure of the vapor component is greatest.
 6. Theprocess according to claim 1, wherein said space is formed by a hoodoverlying said cooling surface, said hood providing an outletcommunicating with said space, step C comprising conducting saidcollected waste air through said outlet; and step D comprising causingsaid vaporous component to crystallize on surfaces located within saidhood.
 7. Apparatus for cleaning waste air generated during thesolidification of molten material, comprising:means for converting themolten material into pieces; a cooling belt for receiving the pieces andallowing the pieces to solidify; a hood overlying said belt andincluding a suction outlet for collecting waste air which contains avaporous component emanating from the material, said hood communicatingwith a cleaner for conducting the waste air to the cleaner; and anarrangement of surfaces disposed within said hood upstream of saidsuction outlet and against which said waste air flows so that at leastsome of the vaporous component crystallizes on said surfaces.
 8. Theapparatus according to claim 7, wherein said surfaces are defined byplates arranged to define a serpentine flow path for the waste air. 9.The apparatus according to claim 8, wherein said serpentine flow pathincludes alternating upward and downward flow path segments.
 10. Theapparatus according to claim 7, wherein said serpentine flow pathcomprises horizontal flow path segments traveling alternately indifferent horizontal directions.
 11. The apparatus according to claim 7,wherein said surfaces are heat tempered.
 12. The apparatus according toclaim 7, wherein said surfaces are formed of a heat-conductive materialand carry conduits for conducting a heat exchange fluid to cool thesurfaces.
 13. The apparatus according to claim 7, wherein there is agreater concentration of said surfaces at a region of highest pressureof said vaporous component.
 14. The apparatus according to claim 13,wherein a spacing between successive surfaces is shortest in said regionof highest pressure.
 15. The apparatus according to claim 7 including atransport device to which said surfaces are mounted, said transportdevice arranged to conduct said surfaces across scrapers for scrapingcrystallized material from said surfaces.
 16. The apparatus according toclaim 7, wherein said surfaces are defined by movable endless beltsarranged to move across scrapers for scraping crystallized material fromsaid surfaces.
 17. The apparatus according to claim 7, wherein said hoodincludes air holes of regulatable dimension for controlling a rate ofwaste air flow through said suction outlet.
 18. Apparatus for thesolidification of molten material, comprising:means for converting amolten material into pieces; a cooling belt for receiving the pieces andallowing the pieces to solidify; a hood overlying said belt andincluding a suction outlet for conducting waste air to a cleaner; and anarrangement of surfaces projecting downwardly from an underside of saidhood, said surfaces disposed above said belt and upstream of saidsuction outlet and against which said waste air flows so that a vaporouscomponent of said material crystallizes on said surfaces.
 19. Apparatusfor the solidification of molten material, comprising:means forconverting a molten material into pieces; a cooling belt for receivingthe pieces and allowing the pieces to solidify; a hood overlying saidbelt and including a suction outlet for conducting waste air to acleaner; and an arrangement of surfaces projecting horizontally fromopposite sides of said hood, said surfaces disposed above said belt andupstream of said suction outlet and against which said waste air flowsso that a vaporous component of said material crystallizes on saidsurfaces.